The present disclosure relates to an electric lens, an optical unit, and an imaging device.
Imaging devices that focus an image of an object onto an image sensor using an optical system, and thereby generate a captured image of the object, are being used widely in a variety of fields. The optical system of such an imaging device is made up of a focus optical system for suitably focusing an image of an object onto the image sensor, and a zoom optical system for enlarging the image of the object. In these focus optical systems and zoom optical systems, a movable lens having a variable lens position is used, and by varying the position of the movable lens, the image of the object is focused, and the image of the object is enlarged as appropriate. In such focus optical systems and zoom optical systems, the focusing range and the zoom magnification factor greatly depend on the movable distance of the movable lens, and when attempting to achieve a wider focusing range or a high-magnification zoom, a large movable distance of the movable lens is set.
An example of an imaging device like the above is an endoscopic device as disclosed in JP 2013-61618A, for example. When attempting to achieve a zoom function as described in JP 2013-61618A in a device with fundamental size limitations in the imaging portion where the optical system is provided, such as an endoscopic device, making the allowable movable range of the movable lens are small as possible becomes important for miniaturization. However, if the allowable movable range of the movable lens is small, it may be impossible to achieve high-magnification zoom, and thus various innovations are demanded for further miniaturization.
To achieve miniaturization of the optical system, it is conceivable to use what is called a liquid crystal lens, in which liquid crystal is disposed between two planar lens substrates. This is because by applying an electrical signal to the liquid crystal to vary the refractive index of the liquid crystal, it becomes possible to vary the focal length of the lens without moving the lens itself. However, while the refractive index takes a larger value as the thickness of the liquid crystal increases, the resolution of the transmitted image unfortunately drops as the thickness of the liquid crystal increases. In addition, when attempting to apply such a liquid crystal lens to an imaging device with size limitations as disclosed in JP 2013-61618A, since the liquid crystal lens is additionally added to the optical system of the imaging device, the number of components increases, and further miniaturization may be impossible.
Meanwhile, JP 2005-129158A discloses technology that adjusts the degree of light scattering and convergence by using, in an optical system provided in an optical disc pickup device, a liquid crystal lens in which liquid crystal is provided in a convex lens shape between two spherical concave lenses.